Ability to mint new position at GCR

[rossgalloway]

Description:

From Feddas:
If you're trying to mint at GCR when you already have a position, you have to manually input the number of tokens you want to mint because the "mint at GCR" button takes into consideration the current minted position and the new minting position together instead of only considering the new minting position. In degenerative.finance it only considered current new minting position.
ie. start new minted position -> withdraw some eth so that you can mint more at a lower GCR -> use the withdrawn eth to mint 2nd position = mint at GCR does not give an output.